How the life prisoner managed to escape and get away is not yet clear.

A manhunt was under way for the escaped inmate last night.

He was being held at the high-security Maghaberry Prison near Lisburn.

Valliday was jailed for a minimum of 17 years in 2010 for the murder of west Belfast father-of-two Frank "Bap" McGreevy.

Mr McGreevy (51) was found badly beaten in his flat in Ross Street in the lower Falls area in March 2008.

He died in hospital three days after the attack.

Valliday had been on a "bender" and high on a mixture of drink and drugs at the time of the attack when he battered the former IRA prisoner with a number of weapons, including a pick-axe handle. Other weapons used included two broom shafts, one wooden and one metal.

He was also on the run from the young offenders' centre at Hydebank when he committed the murder.

The killer, who was 20 at the time of the killing, attacked two other men and damaged two cars nearby shortly afterwards. He handed himself into police the following day after his father and uncle threatened to hold him for police if he refused.

When interviewed, Valliday first claimed he got into a fight with Mr McGreevy outside his flat.

He then changed his story, saying he found Mr McGreevy injured inside his home after seeing two men running from the scene.

During his trial Belfast Crown Court heard that during police interviews, Valliday claimed he knew Mr McGreevy was "somehow connected" with the IRA and a number of other people could have been responsible for his killing.

He refused to give names, saying "once I get out I will get killed stone dead, I know what they're like". Valliday also accused Mr McGreevy of being a "killer" connected to the "Provies", a slang term for the Provisional IRA, but he also described the dead man as "a gentleman" .

Handing down a life sentence, Mr Justice Hart said Valliday had "shown no remorse whatever for his crime and I am satisfied that there are no mitigating factors in the case".

Following the sentencing, Mr McGreevy's family issued a statement in which they said they were "relieved that justice had been done".

Police have appealed to the public to contact the non-emergency number 101 should they spot Valliday or know of his whereabouts, and not to approach him under any circumstances.